How long should a bridge be required to ligate two single strand DNA - Post questions and discuss DNA techniques and protocols such as DNA extraction, PCR, and the study of DNA-binding proteins.

I want to create a DNA library by synthesizing oligos carrying degenerate codons. Because it is impossible that synthetic Oligos provide enough long annealling sequence at both ends for PCR assembly,I would like to directly ligate the oligos with help of a short bridge. Does anybody have experiences? I wonder how long a bridge sequence that is able to anneal to 5' and 3' end of two oligos respectively should be so that the ligaion can proceed without problem?